This invention concerns filtration apparatus, and more particularly filters of the type in which a strip or belt of filter media is moved over a perforated plate support in a tank adapted to receive a liquid to be filtered. A vacuum is developed in the space below the perforated plate to draw liquid through the media to filter the liquid. The media is periodically indexed to bring a fresh segment atop the perforated plate and carry the previous segment with its accumulated solids out of the tank.
Such apparatus is typically used with production metalworking transfer lines to filter liquid coolants and machining fluids to remove chips, grit, etc. to allow reuse of the liquid.
The filter media can take the form of a "permanent" fabric belt which is indexed periodically as the belt becomes clogged, each indexed segment cleaned and recirculated. Alternatively, a very lightweight disposable synthetic media strip can be indexed through the tank, each segment of which collected for disposal after use.
The media is often driven with a flight conveyor having chain loops connected by flights extending across the width of the permanent media belt, which flights act to also carry the removed solids such as machining chips out of the tank.
The conveyor can either be attached to the media (in the case of permanent media belts), or merely frictionally engaged to drive the same. The frictional engagement is used with disposable media.
A recurrent problem is the sealing of the media edges to prevent solids from getting under the edges and allowing unfiltered liquid to pass into the vacuum box or to clog the perforated plate.
It has heretofore been proposed to use segments of inflatable tubing which extend along the side edges of the media and which are inflated with air or liquid during filtering and deflated during indexing.
U.S. Pat. No. 4,390,428 issued on Jun. 28, 1983 for a "Filtration Apparatus" shows such an arrangement used with a permanent media belt attacked to a conveyor. This arrangement does not allow the use of disposable media, which is sometimes desirable even with a permanent media filter as described in the above-referenced copending patent applications.
The attachment of the permanent media belt to the conveyors often leads to problems, as the belt may lengthen or shrink when soaked in liquid, to be mismatched in length to the conveyor, this mismatch creating gathering and leakage of unfiltered liquid past the media.
U. S. Pat. No. 4,481,108 issued on Nov. 6, 1988 for a "Belt Filter" describes disposable media strip pulled through the tank and inflatable sealing tubes used to seal the side edges while keeping the side edges flat. The pulling drive does not allow the use of a chain conveyor to move filtered solids out of the tank and the indexing pulling drive is complex and requires manual advance of the media through the tank when replacing a roll of media. Also, the very light weight of the disposable media allows the media to float off the support plate when air bubbles are present, unless sufficient cake is on the media. The flight conveyor functions to counter this tendency.
U.S. Pat. No. 4,747,010 issued on Sep. 27, 1988 for a "Tank Filter with Conveyor Flight Driven Filter Media Belt" describes disposable media frictionally driven with a chain flight conveyor. The disposable media has little body when wet by the liquid, and cannot extend out much from the conveyor contact with gathering and bunching, and eventually wadding under the conveyor chains and flights. This destroys the integrity of the media allowing bypass of unfiltered liquid. Hence, it is not feasible to improve edge sealing with an inflatable seal as in the above patents.
It is an object of the present invention to provide a filter apparatus and method using disposable media of the type using periodically indexed media with improved edge sealing.